linux-kernel - Re: [PATCH] ktest: restore tty settings after closing console

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Date:	Tue, 27 Jan 2015 17:01:29 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Josh Poimboeuf <jpoimboe@...hat.com>
Cc:	Satoru Takeuchi <satoru.takeuchi@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ktest: restore tty settings after closing console

On Tue, 27 Jan 2015 12:10:04 -0600
Josh Poimboeuf <jpoimboe@...hat.com> wrote:

> When ktest runs the console program as a child process, the parent and
> child share the same tty for stdin and stderr.  This is problematic when
> using a libvirt target.  The "virsh console" program makes a lot of
> changes to the tty settings, making ktest's output hard to read
> (carriage returns don't work).  After ktest exits, the terminal is
> unusable (CRs broken, stdin isn't echoed).
> 
> I think the best way to fix this issue would be to create a
> pseudoterminal (pty pair) so the child process would have a dedicated
> tty, and then use pipes to connect the two ttys.  I'm not sure if that's
> overkill, but it's far beyond my current Perl abilities.

And beyond mine too. I tried to get that right a few times, and it
never worked out. Maybe someone with more oyster skilz can fix this.

> 
> This patch is a much easier way to (partially) fix this issue.  It saves
> the tty settings before opening the console and restores them after
> closing it.  There are still a few places where ktest prints mangled
> output while the console is open, but the output is much more legible
> overall, and the terminal works just fine after ktest exits.

Thanks, I'll add this, and make sure that it doesn't break anything, as
I use ktest daily.

-- Steve

> 
> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
> ---
>  tools/testing/ktest/ktest.pl | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/tools/testing/ktest/ktest.pl b/tools/testing/ktest/ktest.pl
> index b9cd036..ba20f89 100755
> --- a/tools/testing/ktest/ktest.pl
> +++ b/tools/testing/ktest/ktest.pl
> @@ -178,6 +178,7 @@ my $checkout;
>  my $localversion;
>  my $iteration = 0;
>  my $successes = 0;
> +my $stty;
>  
>  my $bisect_good;
>  my $bisect_bad;
> @@ -1349,6 +1350,9 @@ sub open_console {
>  
>      my $flags;
>  
> +    # save terminal settings
> +    $stty = `stty -g`;
> +
>      my $pid = open($fp, "$console|") or
>  	dodie "Can't open console $console";
>  
> @@ -1368,6 +1372,9 @@ sub close_console {
>  
>      print "closing!\n";
>      close($fp);
> +
> +    # restore terminal settings
> +    system("stty $stty");
>  }
>  
>  sub start_monitor {

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